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Chart Builder

The Chart Builder lets you create visualizations of the data sent to Sematext. It lets you build charts for metrics and logs. Charts created through the builder are added to your dashboards and reports as dashboard components. Configuring a chart requires specifying a list of series with metrics, optional filters, and groupings. Charts built through the builder give you insight into spikes and trends, helping you to understand how your infrastructure or applications behave now or how they behaved in the past.

You can display many series on a single chart. Each of them can be configured to have its own color and style:

  • bar
  • line
  • area
  • points

Each series should be configured in a series configuration panel. The panel where you change the settings of each series is split into a couple of sections.

Data source

With Chart Builder you can create charts and other visual components for all App types available in Sematext. We support Monitoring, Logs, Experience and Synthetics. This gives you huge flexibility when building your own dashboards. It is possible to build a single chart which contains data series from Apps of different types, making it possible to visualize for example a correlation of CPU usage on a host with Error logs or user satisfaction. You can place such a chart on a dashboard.

Chart builder data source

Metric names

In the Metrics section you pick one or more metrics which are used to build a data series. If you pick more than one metric you have to apply transformations to let Chart Builder know what's the relationship between the metrics. If you don't write your own transformation expression then all metrics are added to each other producing a single series.

Chart builder metrics

On the list of metrics you can find a special metric count(). This metric is available for Logs and represents the number of matching logs.


Transformations are used to modify metrics with a formula. Why is this useful? Imagine you collect all individual types of CPU usage separately, like os.cpu.user, os.cpu.system, os.cpu.wait. If you want to chart all of them as a single series you can added them up using an expression like this:

os.cpu.user + os.cpu.system + os.cpu.wait

Chart builder transformations

Another example is ratio. Imagine that you are interested in the ratio of the network input traffic and output traffic so you can easily spot suspicious behavior in the system, like a sudden jump of output traffic which does not correlate with the input traffic. In this case you would divide one metric by another to get the required series: /

Math operators

Now you know why transformations are needed. Here is what you can use to build transformations.

We support math operators +, -, *, /, %. Parts of the expressions can be scoped with parentheses (). Here's an example:

os.cpu.user / (os.cpu.user + os.cpu.system + os.cpu.wait) 


In addition to math operations, there are functions you can use. The list of functions will grow over time.


Returns an alternative value if the main argument is NULL.


ifNull(x, y)


ifNull(`os.disk.usage`, 0)


Checks from left to right whether NULL arguments were passed and returns the first non-NULL argument. This function takes any number of parameters.


coalesce(x, y, ...)


Consider you collect two different metrics with a similar meaning. On one host you collect a metric called os.disk.usage and on the second host you collect a metric called os.disk.used. You'd like to show a total disk usage from these two hosts. Unfortunately, metrics are named differently. This is where coalesce comes handy. You simply call the function coalesce(`os.disk.usage`, `os.disk.used`, 0). Depending on the metrics' name for a given datapoint one of os.disk.usage, os.disk.used and 0 will be picked.

Filter by

The Filter section is used to specify criteria that are used to find matching data points. Suppose you collect data from multiple hosts but you'd like to see a chart containing only two of them (host1 and host2). You have to pick the right filter in the Filter by section. You would choose tag name and two tag values host1 and host2.

You can use variables as tag values so they can be configured dynamically from the report level.

Chart builder filters

Group by

In the Group by section you choose what data series to group on the graph. For example, if you choose the tag and for the aggregation in Aggregation field you choose all separately the chart will show a data series for each host separately. Each data series is made up of the selected metric on a particular host.

You can use variables as tag values so they can be configured dynamically from the report level.

Chart builder group by

Aggregation functions

Let's get back to the example from the section above. If you choose aggregation function instead of all separately only one data series is created for all the hosts. The result depends on the aggregation function you choose. The aggregation function determines how the metrics are aggregated into a single data series. You can pick one of avg, sum, min, max.

Rollup by

Data points sent to Sematext Cloud have a time label. If a metric is updated every 10 seconds, and you are looking at a 24-hour time range, you need 14,400 points to display all data points. Displaying so many data points on the chart would make it unreadable and would negatively impact your web browser's performance. If we build time buckets each containing 600 data points we will have 24 data points to display on the chart, one data point for each hour. The Rollup function controls how time buckets are built, meaning what aggregation is performed. You can pick one of avg, sum, min, max as a rollup aggregation function.

Each of the predefined metrics has its own default rollup function defined depending on the type of the metric. All gauge metrics use the avg rollup function and all counter metrics use sum rollup function. In some cases it makes sense to customize the setting.

NOTE: Recommended for expert users.

Chart builder rollup by


Variables are used to dynamically filter and group components by tags.

Filters from the Filter by section don't have to be configured statically when a chart is created. Sometimes you need charts on the dashboard to react to a global filter change.

Consider a case where you're troubleshooting a system and you realize that one of the hosts has problems. You have a dashboard that displays aggregate information for all hosts. You can, of course, reconfigure all dashboard charts (aka components) so they show data only for the host you're interested in. As you might expect this is not a very efficient way to troubleshoot. This is where Variables come into play.

Variables can be created by selecting the "Manage variables" option in Report settings. You can create a tag variable that points to the field.

Manage Variables

A variable is automatically added on top of the dashboard. A variable becomes a drop-down component from which you can select tag values and charts automatically react on the change.

Once the variable is defined it should be added to charts that should react to variable changes. Variables can be used both in the Filter by section and in the Group by section in Chart Builder.

Suppose you have a dashboard with charts that show aggregated metrics about disk usage on several hosts. You want to troubleshoot a problem you've spotted on one of the charts that looks like a small jump in disk usage. To identify the root cause you can try to find the problem by grouping metrics by the tag. A group variable can let you do that from the dashboard level without changing the definition of the series in any of the charts. Now imagine that you've grouped data by but still don't see any obvious problems because the disk usage jumped on all hosts. You may then decide to also group by os.disk and by doing so you may realize that the problem was only with /dev/nvme0n2 disks.


In the style tab, you configure what the chart looks like. You can select bar, line, area and point charts. In addition to the chart type, you can choose a color from the palette and group color scheme. The main goal of a group color scheme is to determine the colors of the series from the same group. When you group a metric by as a result you get a couple of series. Each series can get a different color.

Chart builder styles

A very important feature in the styles tab is the "Stacked" option. When you select the checkbox data of a given series is stacked. This is very useful for area and bar charts. Below you can see a comparison of stacked and non-stacked bar charts.

Chart builder styles

Component Switch

You can switch between different kinds of component visualization types.

Chart builder component switch list

E.g.: You can switch Timeseries to Pie Chart directly from the Chart Builder to see how the data series will be represented in each of them.

Chart builder component switch


Heatbar is a single-line heatmap that is shown above the main, time-series chart.
You can style any series as a heatbar, but it's especially suitable for events and logs.

Here you can see a time-series chart which shows the total number of logs and, above it, a heatbar which tracks only errors among them.

Heatbars example

A chart can have multiple series configured as heatbars, like in the following example:

More than one Heatbar

If all of the series are heatbars the main time-series chart is not even shown.
For example, the following chart is configured to show a single heatbar series, CPU User grouped by OS Host:

Just heatbars

The chart shows six heatbars because the CPU User metric was reported by six different OS Hosts during the observed time range.

Creating Heatbars

Let's build the Usage logs with errors component together.

Since the total number of logs is not particularly interesting, we'll monitor a certain subset of logs, for example logs which contain the word Usage.
We'll have our time-series chart tracking all Usage logs and additionally, we'll use a heatbar to track only errors, like we've seen in the first Heatbar example above.

In your dashboard, click on the Add component button on the top of the screen, which looks like this:

Add component

In the first dialog choose Time Series Chart:

Time-series chart

Then choose Logs data series:

Logs data series

If you're creating your first chart, the initial result may look intimidating at first glance:

New chart

It's just a matter of choosing what we want our chart to show. So far we've chosen a type of chart, but haven't specified which App to use as the source of data and which metric from that App to show.

In the App field, choose any Logs App that contains data and in the Metric field choose a special function count(), which represents the number of logs. We'll name this data series Usage logs, so type that into the Label field.

Great, errors are gone and we already see data in our chart preview:

Chart shows data

Let's keep things organized, change the Custom chart title in the upper left corner to Usage. You just need to click on the title to edit it in-place.

Next, in the Filter by section, shown below, we are going to add a filter to our data series by typing Usage into the Query field. When you're done typing, you can apply the change with the Enter key (while the cursor is still in the Query field) and the chart will be updated, now containing only those logs which matched the query.

Enter query

So far so good, we can see our Usage logs in the chart preview.

Now let's add a heatbar.
Duplicate Usage logs series using the series action menu (...), like this:

Duplicate Usage logs DS

Change the label of the new series to Errors.

Expand the Filter by section, under the Label. As you can see in the screenshot below and hopefully in your own chart, our query: Usage is still here, duplicated correctly from the first series. We'll additionally filter logs to only those with severity: error:

Filter to error severity

Finally, switch to the Style section of our second data series in the upper right corner and change its type to heatbar and color to red.

Changing data series type

And just like that, we have our Usage chart with a heatbar of Usage errors.

Final result

Accessing data in Heatbars

Clicking on a heatbar square opens a panel with a list of Usage errors from the corresponding time range.